This invention relates to a color display apparatus with a display panel, for example, of the liquid crystal type, and more particularly to a color display apparatus which is capable of displaying patterns, such as characters, of a good quality and with a limited number of pixels.
A color display panel constructed, for example, with a liquid crystal material has color dots of the three primary colors (R, G and B) formed thereon in a predetermined order, wherein a color pixel is usually constituted by three adjacent ones of the color dots respectively corresponding to the three primary colors. In this case, the assignment of the combinations of color dots of the three primary colors on the display panel to the respective color pixels on the same panel is fixed in accordance with a rule determined in dependence on the kind of panel. With this kind of color display panel, a pattern such as a character is displayed in a display unit which is a matrix of a predetermined number of pixels.
In recent years, there has been an increase in the number of color display panels of the active-panel type in which a TFT is used for each display dot. In a color display panel of the above type, the upper limit of the resolution is of the order of 720.times.240 color dots (i.e., of the order of 240.times.240 pixels since a pixel is formed by three color dots). This is because it is difficult to form a greater number of TFTs on a broad surface of a panel without suffering a decrease in the yield rate of the panels. However, with a color display panel having a resolution of the above order it is still possible to display a PAL or an NTSC television picture of a sufficiently good quality and to display information such as characters of a good quality provided that the characters are large in size.
In recent years there has been a demand for a liquid crystal display panel of the above type which can be used not only to display a television picture, but also to display character information, for example, via a character broadcasting or a teletext. In the case of the European teletext, it is necessary to display about forty characters in the horizontal direction. Since the number of pixels in the horizontal direction is about 240, even in the recent liquid crystal color display panels as described earlier, the number of pixels for each character in the horizontal direction must be restricted to about five in order to display all the characters, that is to say, the number of color dots in the horizontal direction must be restricted to about fifteen.
FIG. 5 is an illustration showing an enlarged portion of a display panel of the conventional liquid crystal color display apparatus, the portion shown corresponding to one character. In the display panel, shown, a number of color dots (720 color dots in this example) of the three primary colors are arranged in the order of a red (R) color dot 2r, a green (G) color dot 2g and a blue (B) color dot 2b in a cyclic fashion in the horizontal direction, and a number of color dots (240 color dots in this example) of the same color are formed in the vertical direction, whereby a dot matrix is formed in which the color dots of the three primary colors are distributed entirely and uniformly on the panel. In each horizontal line, each color pixel 3 is formed by a respective one of the combinations of three adjacent color dots, namely, a red (R) color dot 2r, a green (G) color dot 2g and a blue (B) color dot 2b which are arranged in this order from left to right, whereby a color pixel matrix, for example, of 240.times.240 is formed on the panel as a whole. With this conventional display apparatus, one character (for example, the character A in FIG. 5) is displayed in a 5.times.9 color pixel matrix. In this case, the display apparatus has a memory 4 in which the respective character patterns are stored in the form of 5.times.9 bit patterns as shown in FIG. 6 (only the bit pattern for the character "A" is shown in FIG. 6). Those color dots 3 corresponding to bits "1" in the bit pattern (i.e., the color dots indicated by hatching in FIG. 5) are activated to display the character.
The above described conventional liquid crystal color display apparatus is disadvantageous in that, since the number of pixels per each character is small, slant segments of a displayed character are significantly uneven (see the slant segments of the character "A" at both of its shoulder portions in FIG. 5). It has thus been practically impossible to display a character of a good quality.